Gas‐phase reaction pathways for
GeH4
decomposition are proposed and the relevant reaction rates are evaluated by transition‐state theory with molecular structures and thermochemical data predicted by ab initio molecular orbital calculations, specifically Hartree‐Fock with second‐order Møller‐Plesset perturbation theory. Pressure and temperature effects are included in computed unimolecular reaction rates through the application of Rice‐Ramsperger‐Kassel‐Marcus theory. Quantum‐Rice‐Ramsperger‐Kassel theory is used to estimate the relative rates of stabilization and chemical activation pathways for the insertion of
GeH2
into
GeH4
to form
Ge2H6
and
Ge2H4
, respectively. The predicted and measured reaction rates agree well with reactions for which experimental kinetic data have been reported. The developed
GeH4
decomposition mechanism is subsequently used in a finite‐element reactor simulation of germanium deposition to demonstrate the utility of quantum chemistry for developing kinetic rates required in realistic macroscopic models of deposition processes. Contribution of gas‐phase reactions to the germanium growth rate is predicted to be important at pressures higher than 1 Torr and temperatures greater than 1000 K.
Silicon epitaxial growth with SiH2C12 (DCS) is modeled within a realistic therma]-fluid environment using a detailed reaction mechanism. The proposed reaction mechanism includes both gas-phase and surface reactions. It accounts for surface-adsorbed species and individual surface coverages to predict deposition rates. The predicted deposition rates are compared to measured growth rates at different temperatures, pressures, and DCS flow rates. The agreement between predicted and measured growth rates is found to be very good. The suggested reaction mechanism is based on two reaction pathways. First, DCS adsorbs directly on the Si surface and decomposes there while desorbing H2, HCI, and SiCl2. Second, at temperatures above 800~ the thermal activation gets high enough to allow the pyrolysis of DCS to SiCI2 and H2 in the gas phase. The generated SiCl2 reacts on the silicon surface, representing the second deposition pathway. The two reaction pathways are valid for all temperatures. The dominance of one or the other pathway at a given temperature results self-consistently from the different thermal activation of the individual chemical reactions involved.
Lattice diffusion and surface segregation of B during growth of SiGe heterostructures by molecular beam epitaxy: Effect of Ge concentration and biaxial stress
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